Summary: Title: Multiscale dynamics to study functional selectivity in GPCRs Upon binding to agonists G protein-coupled receptors (GPCRs) mediate multiple signaling pathways by coupling to intracellular transducer proteins such as G proteins and/or ?-arrestins. Certain agonists exhibit bias in their efficacy to specific signaling pathways. Such biased ligands provide precise therapeutic benefits with fewer side effects as drugs compared to today's GPCR-targeted drugs. There are very few biased ligands known for GPCRs because designing biased agonists is a daunting experimental challenge. Additionally, there is a serious lack of understanding of how GPCRs modulate their functional selectivity for their cognate G-protein in cells. The functional selectivity of GPCRs stems from their dynamics and therefore requires techniques that probe into receptor dynamics to provide a structural basis for functional selectivity. Hence we propose to combine two state-of-the-art dynamics techniques, such as multiscale molecular dynamics (MD) method and genetically coded FRET sensors that are needed to provide dynamic information and understanding of functional selectivity. Building on the successes of developing these techniques, we propose to (1) use computational methods and concurrent experiments to identify the amino acid residues in Gs, Gi and Gq coupled biogenic amine GPCRs that confer selectivity to their cognate G-proteins for functional selectivity, (2) to study the effect of various biased ligands for ?2-adrenergic receptor on the role of the residues that govern the functional selectivity for ?-arrestin1. We propose to advance the multi-scale MD method to allow sampling of large scale conformational dynamics and use this method along with experiments to study the role of the intrinsically disordered carboxy terminus of the ?2-adrenergic receptor on the binding to the Gs protein compared to ?-arrestin binding. The outcome of the proposed work is an understanding of the biological process of how GPCRs recognize their cognate G-proteins and ?-arrestins in live cells. Additionally we will have a powerful computational MD method for routinely studying function of intrinsically disordered regions in proteins.